In the field of pulse detonation engines (“PDEs”) it is generally known that such engines operate by producing a series of pulsed detonations within one or more firing tubes of the engine. An oxidant such as atmospheric air and fuel are directed into an inlet of the firing tube and then combusted within the tube. This results in a dramatic pressure rise as a pressure wave of combusted oxidant and fuel moves along the firing tube increasing in velocity to produce a detonation wave that results in very substantial thrust as an exhaust stream passes out of an outlet of the firing tube.
It is also known that PDEs are integrated with traditional turbine engines, wherein the exhaust stream from the pulse detonation engine (“PDE”) is directed to flow into the turbine to drive the turbine. In such turbine hybrid PDEs, it is common that the turbine typically drives a compressor to force air into one or more of the firing tubes within the PDE.
While such PDEs have tremendous potential for efficient use of fuel and production of enormous thrust per unit mass of the PDE, they nonetheless also have many challenges that have hindered development of an efficient, long-running PDE for an aircraft or a hybrid turbine PDE for production of electrical power. For example, firing PDE tubes directly into a turbine provides a very efficient system layout or architecture. However, in a typical PDE, firing tubes pulse at different times producing a very unsteady flow of the exhaust stream out of the firing tubes. Additionally, the resulting exhaust stream has an extremely high and uneven temperature with localized temperature spikes, etc. This results in significant structural, thermal and performance duress on the turbine.
Firing directly into the turbine also creates a partial-admission turbine effect, wherein a full force of the exhaust stream from the firing tubes only impacts a partial section of the turbine. Even if the firing tubes discharge around a full annulus of the turbine, the unsteady flow of the pulsed and turbulent exhaust stream has the effect of changing incidence angles with each cycle or pulse. This has the same effect on the turbine as the partial-admission turbine effect resulting from a varying number of firing tubes firing at different times and impacting the turbine. For example, it is known that many PDEs utilize a bundle of firing tubes and activate one, several or all of the tubes to meet varying thrust requirements. Studies of PDEs have shown that unsteady, high-temperature exhaust, while manageable on the basis of an average thermal load, nonetheless has the potential to cause deleterious thermal erosion of turbine air foil surfaces due to high-temperature peaks. It is known that, efficient, long-term operation of turbines requires minimizing vibratory stress. Unfortunately, combining PDEs with turbines imposes great vibratory stress upon the turbine, primarily because of the unsteady, turbulent flow of the exhaust stream at supersonic speeds combined with the fluctuating and extremely high temperatures of the exhaust stream.
Therefore, there is a need for a pulse detonation engine that minimizes structural, thermal and long-term, operational duress upon a turbine driven by an exhaust stream from firing tubes of the pulse detonation engine.